Glass fibres can be produced by melting a glass composition in a melter and drawing them out through the tip plate of a bushing assembly. A bushing assembly is generally in the form of a rectangular box with two pairs of opposite side and end walls forming the perimeter thereof with an opening at the top in fluid communication with the melter. The bottom floor comprises a tip plate which is a plate comprising a multitude of orifices or tips through which the glass melt can flow to form fibres, which are attenuated to reach their desired diameter. To ensure an optimal control of the glass melt viscosity, the temperature of the tip plate must be controlled accurately. The temperature of the tip plate depends on the glass melt composition but is generally well above 1000° C. Because of the extreme working conditions, the various components of a bushing assembly are made of platinum or platinum alloys, typically rhodium-platinum alloys.
The load applied on the tip plate is substantial with, on the one hand, the weight of the glass melt lying on top of it and, on the other hand, the drawing force applied to the fibres below. At temperatures well above 1000° C., it is not surprising that tip plates are sensitive to creep and sagging. In order to increase the production rate, larger tip plates with more numerous tips are being used which increase the problem of creep and sagging. For this reason, beside the use of transverse gussets distributed along the length of the tip plate, a longitudinal central stiffening rib is often provided in the centre of the floor to stiffen the tip plate in the longitudinal direction; this configuration corresponds to having two tip plates in parallel separated by a longitudinal beam in a single bushing assembly. Usually, the two tip plate portions and the central beam are made of a single plate folded appropriately. The central beam may, however, be welded to the centre of the top surface of a single tip plate or to the longitudinal edges of two separate tip plates. Examples of bushing assemblies comprising a central stiffening rib, dividing the floor of the bushing assembly into two tip plates are disclosed in WO2000/001630, WO2009/128749, WO9958460, or EP0931026.
When a bushing assembly is worn out, it must be dismounted, and replaced by a new one. The old bushing assembly can be dismantled, cleaned and a new bushing assembly built using the precious metal thus recovered. Such operation is expensive and requires highly qualified operators. The service time of a bushing is therefore of great economical concern. On the other hand, although recycled, the precious metals used for manufacturing a new bushing assembly are so expensive, that the amount of such materials used in the manufacturing should be minimized.
The present invention provides a new design for bushing assemblies, allowing an efficient reinforcement of the tip plates and excellent homogenization of the molten glass while reducing the amount of expensive alloys used for its manufacturing. This and other advantages of the present invention are presented in continuation.